Age hardenable low alloy steels



United States Patent 3,338,709 AGE HARDENABLE LOW ALLOY STEELS Alan J. Baker, Monroeville, Pa., and Frank J. Lauta,

3,338,709 Patented Aug. 29, 1967 erties set forth inthe following Table II after aging as therein indicated:

Rochester, N.Y.,' assignors to United States Steel Cor- TABLE II ipqoration, a corporation of Delaware 5 0 Drawing. Filed May 26, 1965, Ser. No. 459 116 02 015 t T CVN f d 6 Claims. c1. 75-123 lilqeat T Agtin t ghe i striff ti, 8

O 1'83. men reng p.s.i. c The present invention relates to age hardenable, low +80 100 carbon steels and more particularly to age hardenable, w 1 5h W F 1 5 19 97 low carbon steels having a bainitic or martensitic micro- 1:: 3, 33 5 8 structure characterized by high yield strength combined 3 M900 00 201,000 19 14.5 with good toughness 4 5hr. at 1,000 103,000 174,000 70 30 This application is a continuation-in-part of our copending application Ser. No. 349,463, filed Mar. 4, 1964, 5 now abandoned- A review of the data of Table II indicates that Steel Hemmiore attempts Prodce Steels having hlgh yleld N0. 4, which is within the compositional range of this insert: at 1213. 1.53?ifigaiifffsatt in;-

may of 31 ie stren t in excess 0 .s.i. an ar ties. We have discovered that within certain compositi-on- 20 i valuesgin excess of 60 foobpougds at a1 limits, low carbon steels having a microstructure of foot pounds at o R However the other three haunts or v or mlxtures W111 have hlgh steels which are not within the range of the steel of this strength combined with good toughness 1n the age f invention are deficient either in strength or ductility. fined P The following Table III comparing Steel No. 4 in the m followmg composmonal lumts 111 Percent y air cooled, and air cooled and aged condition, thus havwelght: ing a bainitic structure shows the steel to have somewhat Carbon 05 to 2 better impact values at lower strength than with a marten- Nickel 8 to 10 s1t1c mlcrostructure. Molybdenum .5 to 2.5 Cobalt 3 to 5 TABLE III Manganese, max. .25 2 OH CVN f t d 0. O y Phosphorus, max. .10 setgields Tensile W S Sulphur, max. Aging Treatment Strength, Strength, Silicon max 2 p.s.i. p.s.i. +80 800 F. Aluminum, max. .1 Balance iron and residual impurities. gli ggglgg 122,223 13:32; 1:: L

Other elements may be present in amounts which do n not adversely affect the properties. 40

Steel within such range will have a yield strength within I the range of 150,000 to 200,000 p.s.i. and Charpy V-notch Another heat, identified as Steel 5 of the following values in excess of foot-pounds at F. and 50 composition further illustrates the invention: foot-pounds at 80 to 100 R, if quenched from an Percent austenitizing temperature in the range of 15-00 to 1700- 5 Carbon 0.1-0 F. sufiiciently rapidly to produce a structure of marten- Manganese 0.002 Site or bainite or mixtures thereof and thereafter aged S1l1 n 0.004 Within the range of 800 to 1000 F. for 2 to 5 hours. Nickel 8.96 The examples of the following Table I will serve to Molybdenum .95 illustrate the invention. 50 Cobalt 3.99 These steels were oil quenched from 1700 F. to Aluminum 0.002 develop a microstructure of martensite and had the prop- Balance iron and resldual lmpuritles.

TABLE I Steel N o 0 Mn P S Si N1 Mo 00 Al This steel Was vacuum melted and vacuum carbon deoxidized and had the properties given in the following Table IV after treating as therein indicated:

TABLE IV Charpy V-Notch Yield Tensile Strength, Strength,

p.s.i. p.s.i. +80 80 ft.-1b. it.-lb

Air-cooled 105, 000 147, 000 136 131 Air-cooled and Aged 132, 000 156, 000 135 130 Oil-quenched and Aged (5 hrs. at 1,000 F.). 160, 000 165, 000 119 114 As above indicated, the steel in the air cooled condition had a bainitic microstructure and in the oil quenched condition had a martensitic microstructure.

Steel 6 of the following composition also was vacuum melted, and vacuum carbon deoxidized.

Percent Carbon 0.19 Manganese 0.21 Silicon 0.005 Nickel 8.94 Molybdenum 0.95 Cobalt 4.0-8 Aluminum 0002 Balance iron and residual impurities.

After treating as indicated in the following Table V, Steel 6 exhibited the properties therein set forth:

The air cooled specimens had a predominantly bainitic microstructure and the oil quenched specimens a predominantly martensitic microstructure.

It is thus apparent that the steel of this invention has high yield strength combined with good ductility as indicated by a Charpy V-notch value in excess of 60 footpounds at room temperature and 50 foot-pounds at 80 to --100 F. when quenched to a martensitic microstructure. In the air cooled condition having a bainitic microstructure, the steel has somewhat less yield strength but better impact values. Thus for certain uses where optimum impact values are desired, a bainitic microstructure resulting from slower .air cooling may be desirable. However when the combination of optimum tensile strength and good ductility is required, the steel should be liquid quenched to a martensitic microstructure after austenitizing in the range of 1500 to 1700 F. and aged within the range of 800 to 1000 Rim 2 to 5 hours. Depending on thickness, air cooling or liquid, quenching may develop a microstructure consisting of a mixture of bainite and martensite. In such condition, the strength and toughness will be intermediate those noted hereinabove.

With the composition of this invention, the combination of high strength along with good toughness results from the quenching to a martensitic or bainitic microstructure or mixture thereof, together with a subsequent heat treatment to improve toughness while retaining strength. The retention of strength, after the toughening heat treatment, results from an age hardening reaction brought about by the precipitation of intermetallic compounds.

While we have shown and described several specific embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, .as defined in the appended claims.

We claim:

1. Low carbon, age hardenable steel containing in percent by weight Carbon .05 to .2 Nickel 8 to 10 Molybdenum .5 to 2.5 Cobalt 3 to 5 Manganese, max. .25 Phosphorus, max. .10 Sulphur, max. .10 Silicon, max. .2 Aluminum, max. .1

with the balance iron and other elements in amounts which do not adversely affect the properties.

2. Low carbon steel having a microstructure of the class consisting of martensite, bainite or mixtures thereof characterized in the age hardened condition by a yield strength in excess of 150,000 p.s.i. combined with a Charpy V-notch value in excess of foot-pounds at room temperature and 50 foot-pounds at 80 F., said steel containing in percent by weight Carbon .05 to .2 Nickel 8 to 10 Molybdenum .5 to 2.5 Cobalt 3 to 5 Manganese, max. .25 Phosphorus, max. .10 Sulphur, max. .10 Silicon, max. .2 Aluminum, max. .1

with the balance iron and other elements in amounts which do not adversely affect the properties.

3. Age hardened, low carbon steel having a microstructure of the class consisting of bainite, martensite or mixtures thereof, a high yield point and a Charpy V-notch value in excess of 50 foot-pounds at --80 F., said steel consisting essentially of, in percent by weight with the balance iron and other elements in amounts which do not adversely aifect the properties.

4. Age hardened, low carbon steel quenched to a microstructure of the class consisting of bainite, martensite or mixtures thereof and aged at a temperature between 800 and 1000" F., said steel containing in percent by Weight Carbon .05 to .2 Nickel 8 to 10 Molybdenum .5 to 2.5 Cobalt 3 to 5 Manganese, max. .25 Phosphorus, max. .10 Sulphur, max. .10 Silicon, max. .2

Aluminum, max. .1 with the balance iron and other elements in amoun which do not adversely afiect the properties, said steel being characterized by a high yield strength and a Charpy V-notch value in excess of 50 foot-pounds at 50 F.

5. Low carbon steel having a microstructure of the class consisting of martensite, bainite or mixtures thereof characterized in the age hardened condition by a yield strength in excess of 150,000 p.s.i, combined with a Charpy V-notch value in excess of 60 foot-pounds at room temperature and 50 foot-pounds at 80 F., said steel consisting essentially of, in percent by weight Carbon .05 to .2 Nickel 8 to 10 Molybdenum .5 to 2.5 Cobalt 3 to 5 Manganese, max. .25 Phosphorus, max. .10 Sulphur, max. .10 Silicon, max. .2 Aluminum, max. .1

wili the balance essentially iron.

6. Age hardened, low carbon steel having a microstructure of the class consisting of bainite, martensite or mix- 6 tures thereof, a high yield point and a Charpy V-notch value in excess of foot-pounds at F., said steel consisting essentially of, in percent by Weight with the balance essentially iron.

No references cited.

DAVID L. RECK, Primary Examiner. P. WEINSTEIN, Assistant Examiner.

Notice of Adverse Decision in Interference In Interference No. 96,840 involvin Patent No. 3,338,709, A. J. Baker and F. J. Lauta, AGE HARDENABLE OW ALLOY STEELS, final judg ment adverse to the patentees was rendered June 1, 1972, as to claim 1.

[Official Gazette August 22, 1.972.] 

1. LOW CARBON, AGE HARDENABLE STEEL CONTAINING IN PERCENT BY WEIGHT 